Determination of elements in organic compounds

ABSTRACT

Apparatus for the rapid and automatic determination of elements such as halogen and sulphur in organic compounds comprises a closed vessel; means for introducing into said vessel and for supporting in said vessel a sample of said compound to be analyzed; means for filling said vessel with oxygen; means for causing combustion of said sample; means for causing circulation of an absorption liquid in a closed circuit including said vessel; means for determining and detecting said element to be analyzed in said absorption liquid; means for causing said absorption liquid to contact during the circulation thereof the inner surfaces of said vessel and said means for supporting said sample; and means for causing said circulation to cease when said determination is complete.

United States Patent [191 Pont [ 1 Feb. 13, 1973 [21] Appl. No.: 114,767

[30] Foreign Application Priority Data Feb. 16, 1970 France ..7005445Jan. 4, 1971 France ..7l00030 [52] US. Cl. ..23/230 PC, 23/230 M, 23/253PC, 204/1 T, 204/195 T [51] Int. Cl....G0ln 27/26, GOln 31/06, G0ln31/12 [58] Field of Search ..23/230 PC, 230 M, 253 PC; 204/1 T, 195 TOTHER PUBLICATIONS A. M. G. MacDonald, The Oxygen Flask Method, TheAnalyst, Vol. 86, No. 1018, pages 3-12 (January, 1961 OD71.A45.

Primary ExaminerJoseph Scovronek Attorney-Stevens, Davis, Miller &Mosher [5 7] ABSTRACT Apparatus for the rapid and automaticdetermination of elements such as halogen and sulphur in organiccompounds comprises a closed vessel; means for introducing into saidvessel and for supporting in said vessel a sample of said compound to beanalyzed; means for filling said vessel with oxygen; means for causingcombustion of said sample; means for causing circulation of anabsorption liquid in a closed circuit including said vessel; means fordetermining and detecting said element to be analyzed in said absorptionRelel'ences Cited liquid; means for causing said absorption liquid toUNITED STATES PATENTS contact during the circulation thereof the innersurfaces of said vessel and said means for supporting said 3,529,9379/1970 ll'iara et a1 ..23/253 PC sample; and means for causing saidcirculation to 2,760,922 3/1956 Williams, 0 l T cease when saiddetermination is complete. 3,305,468 2/1967 Liesch ....204/l95 T3,168,377 2/1965 Williams, Jr ..23/230 PC 8 Claims, 3 Drawing FiguresPATENTEDFEB13|973 3.716.334

saw 1 or lrwenlor MICHEL PONT By Jmfim MA: 72%

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PATENTEBFEB! 3,716 334 SHEET 3 UF 3 VIII.

Invenlor MICHEL PONT' I By mymmm A llorneys DETERMINATION OF ELEMENTS INORGANIC COMPOUNDS The present invention provides a rapid and automaticmethod for carrying out the quantitative elementary analysis, in aclosed chamber full of oxygen, of elements such as the halogens(especially chlorine, bromine, and iodine) and sulphur in organiccompounds. This process is especially suitable for elementary analysison the decimilligram scale. The invention also provides an apparatus forthe process.

It is frequently necessary to carry out the determination of halogensand sulphur, especially in the chemical and related industries. Forexample, determinations of chlorine are frequently carried out in themanufacture of copolymers based on vinyl chloride.

The best-known methods of analysis require that the halogens and sulphurshould first be converted into inorganic compounds. In one such method,called the Schoniger method, the compound to be analyzed is burnt in aclosed chamber full of oxygen. This closed chamber method is well suitedto a variety of determinations [see The oxygen flask method" by A. M. G.MACDONALD in The Analyst, January l961, 3 to 12, and Sur la technique deMineralisation de SCHONIGER (On the SCHONIGER technique of conversion toinorganic compounds) by M. REVERCHON in Chimie Analytique, volume 44,No. 8. August 1962]. However, this method has not previously beenoperated automatically.

The present invention provides a method for the quantitative analysis ofelements such as the halogens and sulphur in organic compounds, rapidlyand automatically, which comprises converting by combustion a knownquantity of said compound into inorganic compounds in a zone containingoxygen and an absorption liquid, causing the said absorption liquid tocontact said inorganic compounds, analyzing the said element in saidabsorption liquid which has contacted said inorganic compounds, andcausing the said absorption liquid to cease to contact said inorganiccompounds when said analysis is complete.

As generally operated, the new method comprises converting a knownquantity of the said compound into inorganic compounds by combustion ona carrier in a flask containing an absorption liquid in its lower partand oxygen in its upper part, causing the said absorption liquid tocirculate in a closed circuit and contact the walls of the said flaskand the said carrier thereby absorbing said inorganic compounds, passingsaid circulated absorption liquid through a zone wherein the element tobe analyzed is detected and determined in said liquid, and causing saidcirculation to cease when the said determination is complete.

The new method is conveniently carried out in an apparatus whichcomprises:

a closed vessel;

means for introducing into said vessel and for supporting in said vessela sample of said compound to be analyzed;

means for filling said vessel with oxygen;

means for causing combustion of said sample;

means for causing circulation of an absorption liquid in a closedcircuit including said vessel; means for determining and detecting saidelement to be analyzed in said absorption liquid;

means for causing said absorption liquid to contact during thecirculation thereof the inner surfaces of said vessel and said means forsupporting said sample; and

means for causing said circulation to cease when said determination iscomplete.

Such an apparatus can be connected to devices which cause thedetermination to be effected in a programmed manner, and further todevices which cause the results of the analysis to be measured, recordedand examined.

In more detail the new method is carried out in the following preferredmanner, which refers to the case of the elementary analysis, on thedecimilligram scale, of an organic product containing a halogen. Thematerial on which the determination is to be carried out, which may besolid or liquid, is weighed on a precision balance into an envelope ofnegligible blank value (that is to say containing nothing which caninfluence the result of the determination); this envelope can forexample be made of poly(ethylene glycol terephthalate). The weight ofthe sample is generally between 100 and 2,000 ;/.g depending on thecontent of the element to be determined in the sample. The sealedenvelope, containing the material to be analyzed, is placed on a carrierwhich is introduced into the flask. The latter contains a reducingabsorption liquid in its lower part. The flask and its charge are purgedwith oxygen. The envelope containing the sample is ignited by anyappropriate means, for example by heating to redness an electricalresistance which constitutes the carrier itself, the ends of which areconnected to an appropriate current supply; and the combustion isallowed to go to completion. The sample is thus converted into inorganiccompounds. The duration of this operation is generally between 0.1 and10 seconds. The absorption liquid is then caused to circulate in aclosed circuit and the walls of the flask, and the sample carrier aresprinkled with this liquid. This closed circuit circulation can beachieved by any appropriate means, for example by a pump, a propeller, astirrer, an oscillating device and the like. The circulation of theabsorption liquid simultaneously causes the sprinkling of the walls ofthe flask and of the sample carrier, the absorption and reduction of thecombustion products, and the homogenization of the liquid phase. Thecirculating liquid now contains halide ions. It is circulated throughthe flask several times, the circulation time being generally between 10seconds and 30 minutes and preferably between 1 and 10 minutes. Thespeed of circulation of the liquid in contact with devices fordetermination and detection of halide ions is generally between 1cm/second and cm/second, and preferably between l0 and 50 cm/second. Thehalide is determined by any known process, for example by coulometricdetermination or volumetric determination, and detection may be, forexample, by potentiometric (zero-current or imposed current) oramperometric means. Colorimetry can also be employed. The detectionapparatus indicates the. end of the determination and gives a signal forstopping the circulation of the absorption liquid. The next analysis canthen be carried out, and the absorption liquid can generally be reusedfor a certain number of consecutive determinations. Where halogen isbeing determined by coulometric deposition as silver halide, it isnecessary to shield the liquid and the silver halide from light to avoidphoto-decomposition of the silver halide.

Each operation of the new method can be controlled manually or by anappropriate automatic programming device. Even with manual operation upto 12 determinations per hour can be carried out (not counting the timefor weighing), compared with only three by prior art methods.

The new method can, of course, be applied to the determination ofelements other than halogens. Thus, the method is applicable to thedetermination of any element which can be converted into an inorganiccompound by combustion in oxygen, e.g. sulphur, using an appropriateabsorption liquid and appropriate means of determination and detection.

The three Figures of the accompanying drawings show three forms of theapparatus of the invention. The drawings are not to scale. FIGS. 1 and 2show preferred embodiments especially suitable for determination ofhalogens. FIG. 3 shows a particularly valuable embodiment especiallysuitable for the determination of sulphur.

The apparatus shown in FIG. 1 comprises a flask 1, for example of glass,conveniently of between l and I00 cm volume, and of a spherical shapeslightly elongated towards the bottom. This flask 1 is equipped with twotubes 2 and 3 on each of which there is provided a tap 4 and 5 forfilling with oxygen and purging out the air. The flask 1 is providedwith an orifice 6 which permits the introduction of the sample to beanalyzed, placed in a sealed envelope (not shown) on the carrier 7,which for example consists of several turns of platinum wire. Thisplatinum wire is heated to redness for a moment by connecting the endsof it to a source of current and applying a potential, and this allowsthe envelope and the sample in it to be ignited. The carrier 7, locatedabove the absorption liquid 10, is centered in the flask by means of astopper 9. The flask has two orifices, a lower orifice 11 and an upperorifice 12, connected by a tube 13 outside the flask; this tube canconsist of various materials, such as glass, polyvinyl chloride or asilicone elastomer. A pump 16 can be provided on this tube. This pumpcan be of the peristaltic type if the corresponding part of-the tube 13is made of a flexible material such as a silicone elastomer. Preferably,a centrifugal pump is used, especially if the tubes are made of glass.

A circuit is thus formed, through which the absorption liquid flows inthe direction shown by the arrows. When the absorption liquid enters theflask, in its upper part, it sprinkles the walls of the latter, and thecarrier 7, by virtue of the appropriate shape, for example like asprinkler head, of the device 14 which is centered on the stopper 15. Onthe tube 13 for the circulation of the absorption liquid there arelocated, for example in the case of coulometry, determination electrodesl8 and 19 connected to a direct current generator (not shown), andelectrodes 20 and 21 connected to known detection apparatus (not shown).The group of electrodes can be placed anywhere in the circuit. Whereappropriate, a heat exchanger 17 can also be provided. The apparatus canif necessary be shielded from light, for example by being placed in abox (not shown).

In FIG. 1 the various electrodes are shown as being located in thecircuit through which the absorption liquid flows, in various planeswhich are substantially at right angles to the axis of circulation ofthe liquid. However, the determination electrodes and detectionelectrodes can also all be placed in one and the same plane which issubstantially at right angles to the axis of circulation of the liquid.Such an arrangement is shown in FIG. 3, described in detail below, whichis otherwise generally similar to FIG. 1.

Of course, if a non-electrical method of determination, such ascolorimetry, is used, the electrodes can be omitted, and the appropriatedetermination apparatus is then included in the liquid circulationcircuit.

FIG. 2 shows schematically an alternative embodiment of the apparatus ofthe invention. This apparatus is in the shape of a vertical cylindricalcell 31 with rounded ends. It is provided internally with a cylindricalwall 33 concentric with the lateral wall of the cell, and spaced awayfrom the latter by ties which are not shown. A propeller 32 is locatedin the absorption liquid 35, at the bottom of the internal cylinder 33;this propeller 32 is driven mechanically or electromagnetically by anyappropriate known means. When the propeller 32 is rotated rapidly, theabsorption liquid 35 circulates in a closed circuit in the directionindicated by the arrows, sprinkling the upper part of the flask and thesample carrier 34, by virtue of a drip device 40. The determinationelectrodes 36 and 37 and detection electrodes 38 and 39 are locatedlaterally, as shown in FIG. 2.

An alternative method of igniting the sample on the sample carrier 7 or34 consists of placing near the flask l or 31 a lamp equipped with anoptical device, such as a spherical mirror, which focuses the radiationfrom the lamp onto the sample placed on its carrier. By switching on thelamp, the sample is caused to ignite without having to heat the carrierto redness.

These apparatuses allow rapid and precise analyses to be carried outwithout previous start-up, as is shown by the following Examples.

EXAMPLE I Chlorine is determined in chlorothiazide, of overall formula Cl-I O N S Cl (l, l -dioxo-6-chloro-7-sulphamoyl-benzo-l-thia-2,4-diazine).

The apparatus used is that shown in FIG. 1; it is shielded from light byplacing inside a box. The heat exchanger 17 is not used. The volume ofthe flask l is 60 cm. The absorption liquid circuit 13 consists of glasstubes of 2 mm internal diameter, and silicone elastomer tubes of 3 mminternal diameter.

The determination is carried out by the coulometric method usingelectrodes 18 and 19 and the detection by the potentiometric methodusing electrodes 20 and 21. The electrode 18 is of platinum and dipsinto a solution of potassium sulphate, separated from the circuit by aporous partition; the electrode 19 is of silver. These two electrodes 18and 19 are connected to the coulometric determination apparatus. Theindicator electrode 20, which is of silver, and the reference electrode21, of mercurous sulphate, are connected to the potentiometric detectionapparatus. The determination electrode 19 is close to, and upstreamfrom, the indicator electrode 20, as shown in FIG. 1 (with theabsorption liquid circulating in the direction of the arrows). Thisarrangement makes it possible not to exceed the end point of thedetermination, i.e. the coulometric determination is stopped immediatelyas the electrodes 20 and 21 indicate a predeterminate concentration ofAg ions in the absorption liquid.

An analysis is carried out as follows. First, cm of a reducingabsorption solution are introduced into the flask; the solution is madeup by mixing 25 cm of an aqueous solution of potassium hydrogen sulphate(pH 1.4), 25 cm of an 0.4 percent by weight aqueous solution ofhydrazine sulphate and 1 cm of an 0.3 percent strength solution ofgelatine in water-methanol (3 volumes of water per 7 volumes ofmethanol). The sample to be analyzed is weighed into a poly(ethyleneglycol terephthalate) envelope and the envelope is sealed with hotnitrogen (the envelope is produced from a film of 50 microns thicknessand weighs 2.5 i- 0.5 mg). The sealed envelope, containing the sample,is now placed on the carrier 7 and introduced into the flask 1, and thetaps 4 and S are operated so as to fill the flask with oxygen. Thesetaps are closed, and the platinum coil of the carrier is subjected to anelectric potential so as to bring it to redness for just sufficientlylong to cause the envelope and the sample to ignite. When the combustionis complete, the peristaltic pump 16 and the determination and detectionsystems are started.

The circulation of the absorption liquid causes the flask and thecarrier to be sprinkled, and the halide to be homogeneously distributedin the absorption liquid and accurately determined. The determinationstops automatically at the end point, signalled by the detectionapparatus comprising'electrodes 20 and 21 which stops the circulation.

The Table given below summarizes the results the results of thedetermination of chlorothiazide in the case of 17 successive analysescarried out with the same absorbing solution. The theoretical chlorinecontent of chlorothiazide is l 1.99 percent.

These 17 operations require only 1 hour and 30 minutes (excluding thetime of weighing). The same series of determinations carried out by theconventional method, without recirculation of the absorption liquid,require 6 hours.

EXAMPLE 2 The determination of bromine in p-bromobenzoic acid, C,H .,OBr, is carried out. The same apparatus as in Example 1, and an absorbingsolution of the same composition and in the same amount as in Example 1,are used. As the determination takes place at 35C., the heat exchanger17 is used. The procedure is in all respects similar to that describedin Example 1.

The Table below summarizes the results obtained in the case of 10successive determinations using the same absorbing solution. Thetheoretical bromine content of p-bromobenzoic acid is 39.75 percent.

Weight of the sample Bromine of p-bromobenzoic acid in pg found 431.039.76 854.0 39.76 398.4 39.79 677.2 39.70 281.8 40.06 374.4 40.06 372.739.74 425.3 39.38 298.1 39.46 456.7 39.74

These determinations take 1 hour 30 minutes (excluding the time ofweighing), while the conventional process without recirculation requires3 hours 30 minutes.

EXAMPLE 3 The determination of sulphur in dihydroxydiphenylsulphone, CI- 0 s, is carried out. The apparatus shown in FIG. 3 is used. The flask1 has a volume of 60 cm. The absorption liquid circuit 13 consists ofglass tubes of 4 mm internal diameter which form a closed loop, andcomprises a centrifugal pump made of glass 56, the rotor of whichconsists of a bar magnet coated with polytetrafluoroethylene.

The determination is carried out by a coulometric method usingelectrodes 58 and 59 and the detection by a method in which the pH ismeasured using glass electrode 60. The electrode 58 of silver dips intoa 20 percent aqueous sodium chloride solution contained in a bent tube53 and kept separated from the circuit 13 by a porous ceramic plug 52.The electrode 59 of platinum is arranged at right angles to the axis ofcirculation of the absorption liquid, opposite the end of the bent tube53. The two electrodes 58 and 59 are connected toa coulometricdetermination apparatus (not shown). The glass electrode 60 (in which areference electrode and a measuring electrode are grouped together intoa single electrode of small size) provides the means of detection. Thiselectrode 60 is connected to a pH-meter (not shown), which controls thecoulometric determination apparatus.

The determination electrodes 58 and 59 are arranged upstream from thedetection electrode 60, as shown in the Figure. (The absorption liquidcirculates in the direction of the arrows). This arrangement makes itpossible not to exceed the determination end point.

Analysis is carried out as follows. First, 20 cm of an absorbingsolution 50 containing 20 percent of sodium chloride in water, and 1 cmof 10 percent by weight hydrogen peroxide, are introduced into theflask 1. The sample to be analyzed is weighed into apoly(ethylene glycolterephthalate) envelope which is sealed with hot nitrogen, the envelopebeing produced from a film 50 microns thick, and weighing 2.5 i 0.5 mg.The sealed envelope containing the sample is then placed on the carrier7 and introduced into the flask. The flask is closed, and a programmer(not shown) is started, which automatically triggers the operation ofthe taps 4 and for filling the flask with oxygen. With these tapsclosed, the programmer applies a potential to the platinum coil of thecarrier 7, so as to heat it to redness for just sufficiently long toignite the envelope and the sample. When the combustion is complete, theprogrammer starts the centrifugal pump 56 and the determination anddetection systems. The circulation of the absorption liquid causes thewalls of the flask, and the carrier 7, to be sprinkled from the device14 which acts as a sprinkler head. This circulation causes the sulphuricacid formed to be uniformly distributed in the absorption liquid andpermits its determination, followed by the detection apparatus whichdetects the end of the determination, i.e. the return to apredeterminate pH of the circulating liquid.

The Table below summarizes the results of the determination of dihydroxydiphenylsulphone, for successive analyses'carried out with the sameabsorbing solution. The theoretical sulphur content ofdihydroxydiphenylsulphone is 12.81 percent.

Weight of the sam 1e of S, dihydroxydipheny sulphone found in #2 These10 determinations only require 55 minutes (not including the weighingtime). The same series of determinations carried out by a conventionalmethod require 3 hours 30 minutes.

EXAMPLE 4 The Table below summarizes the results obtained in the case of10 consecutive determinations, using the same absorbing solution.Dimethylsulphoxide has a theoretical sulphur content of 4 1 .04 percent.

Weight of the sample of S, dimetlgylsulphoxide in pg found 55.0 41.34524.2 41.27 528.7 41.25 465.6 41.03 580.7 41.35 486.5 41.05 420.3 41.61621.9 40.93 612.2 41.24 848.3 40.85

The 10 determinations take 1 hour (not including the weighing time),while, if the absorption liquid is not recirculated, the time requiredis 3 hours 30 minutes.

lclaim: l. A method for the quantitative analysis of an element in anorganic compound which comprises converting a known quantity of the saidcompound into inorganic compounds by combustion on a carrier in a flaskcontaining an absorption liquid in its lower part and oxygen in itsupper part, causing the said absorption liquid to circulate in a closedcircuit and contact the walls of the said flask and the said carrierthereby absorbing said inorganic compounds, passing said circulatedabsorption liquid through a zone wherein the element to be analyzed isdetermined and wherein the end-point of the determination is detected,and causing said determination to cease when said end-point is reached.

2. A method according to claim 1 in which the said element is determinedelectrolytically in said absorption liquid.

3. A method according to claim 1 in which the element is chlorine,bromine, iodine or sulphur.

4. Apparatus for the quantitative analysis of an element in an organiccompound which comprises:

a closed vessel;

means for introducing into said vessel and for supporting in said vessela sample of said compound to be analyzed;

means for filling said vessel with oxygen;

means for causing combustion of said sample;

means for causing circulation of an absorption liquid in a closedcircuit including said vessel;

means for determining said element to be analyzed in said absorptionliquid;

means for detecting the end-point of the determination in saidcirculating absorption liquid;

means for causing said absorption liquid to contact during thecirculation thereof the inner surfaces of said vessel and said means forsupporting said sample; and

means for causing said determination to cease when said end-point isdetected.

5. Apparatus according to claim 4 in which means are also provided forheat-exchanging said absorption liquid during circulation thereof.

6. Apparatus according to claim 4 in which the means for supporting thesaid sample and the means for causing combustion of the said sample is aplatinum wire carrier which can be heated to redness electrisaid Ocally.

1. A method for the quantitative analysis of an element in an organiccompound which comprises converting a known quantity of the saidcompound into inorganic compounds by combustion on a carrier in a flaskcontaining an absorption liquid in its lower part and oxygen in itsupper part, causing the said absorption liquid to circulate in a closedcircuit and contact the walls of the said flask and the said carrierthereby absorbing said inorganic compounds, passing said circulatedabsorption liquid through a zone wherein the element to be analyzed isdetermined and wherein the end-point of the determination is detected,and causing said determination to cease when said end-point is reached.2. A method according to claim 1 in which the said element is determinedelectrolytically in said absorption liquid.
 3. A method according toclaim 1 in which the said element is chlorine, bromine, iodine orsulphur.
 4. Apparatus for the quantitative analysis of an element in anorganic compound which comprises: a closed vessel; means for introducinginto said vessel and for supporting in said vessel a sample of saidcompound to be analyzed; means for filling said vessel with oxygen;means for causing combustion of said sample; means for causingcirculation of an absorption liquid in a closed circuit including saidvessel; means for determining said element to be analyzed in saidabsorption liquid; means for detecting the end-point of thedetermination in said circulating absorption liquid; means for causingsaid absorption liquid to contact during the circulation thereof theinner surfaces of said vessel and said means for supporting said sample;and means for causing said determination to cease when said end-point isdetected.
 5. Apparatus according to claim 4 in which means are alsoprovided for heat-exchanging said absorption liquid during circulationthereof.
 6. Apparatus according to claim 4 in which the means forsupporting the said sample and the means for causing combustion of thesaid sample is a platinum wire carrier which can be heated to rednesselectrically.
 7. Apparatus according to claim 4 for the quantitativeanalysis of a halogen in which the said means for determining saidelement comprises two electrodes, one of which is made of silver, andthe said means for detecting the end-point of the determinationcomprises two potentiometric electrodes.